linux-kernel - Re: [PATCH 1/2] kasan: add ability to detect double-kmem_cache

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Date:   Fri, 19 Nov 2021 15:25:38 +0100
From:   Vlastimil Babka <vbabka@...e.cz>
To:     Marco Elver <elver@...gle.com>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Andrey Ryabinin <ryabinin.a.a@...il.com>,
        Alexander Potapenko <glider@...gle.com>,
        Andrey Konovalov <andreyknvl@...il.com>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Christoph Lameter <cl@...ux.com>,
        Pekka Enberg <penberg@...nel.org>,
        David Rientjes <rientjes@...gle.com>,
        Joonsoo Kim <iamjoonsoo.kim@....com>,
        kasan-dev@...glegroups.com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org
Subject: Re: [PATCH 1/2] kasan: add ability to detect
 double-kmem_cache_destroy()

On 11/19/21 15:22, Marco Elver wrote:
> Because mm/slab_common.c is not instrumented with software KASAN modes,
> it is not possible to detect use-after-free of the kmem_cache passed
> into kmem_cache_destroy(). In particular, because of the s->refcount--
> and subsequent early return if non-zero, KASAN would never be able to
> see the double-free via kmem_cache_free(kmem_cache, s). To be able to
> detect a double-kmem_cache_destroy(), check accessibility of the
> kmem_cache, and in case of failure return early.
> 
> While KASAN_HW_TAGS is able to detect such bugs, by checking
> accessibility and returning early we fail more gracefully and also
> avoid corrupting reused objects (where tags mismatch).
> 
> A recent case of a double-kmem_cache_destroy() was detected by KFENCE:
> https://lkml.kernel.org/r/0000000000003f654905c168b09d@google.com
> , which was not detectable by software KASAN modes.
> 
> Signed-off-by: Marco Elver <elver@...gle.com>

Acked-by: Vlastimil Babka <vbabka@...e.cz>

> ---
>  mm/slab_common.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/mm/slab_common.c b/mm/slab_common.c
> index e5d080a93009..4bef4b6a2c76 100644
> --- a/mm/slab_common.c
> +++ b/mm/slab_common.c
> @@ -491,7 +491,7 @@ void kmem_cache_destroy(struct kmem_cache *s)
>  {
>  	int err;
>  
> -	if (unlikely(!s))
> +	if (unlikely(!s || !kasan_check_byte(s)))
>  		return;
>  
>  	cpus_read_lock();
>